* docs(#2197): drop --validate docs for /gsd-plan-phase and /gsd-execute-phase
These two commands never parse --validate (silent no-op); the flag is
real only for /gsd-quick. Remove the false flag-table rows and CLI
examples across COMMANDS.md and the how-to guides (en + ja-JP/zh-CN/
ko-KR/pt-BR mirrors), and correct the manager.flags.execute example
from --validate to --cross-ai (a flag execute-phase actually parses).
/gsd-quick's real --validate docs are left untouched.
Ref #2197
* docs(#2197): add changeset for --validate docs removal
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Co-authored-by: CI Rebase Check <ci@gsd-redux>